You can use a variety of apps to add a live clock to your Mac's desktop wallpaper background. Each app has it own style, features and settings.
Check out How To Add a Clock To Your Mac Desktop at YouTube for closed captioning and more options.
World Clock App For Desktop
Free World Time Clock Desktop Mac
The 'Desktop Clock' app puts a beautiful and practical clock on your Mac's desktop and Dock. The app offers 23 beautiful designs to choose from depending on your taste and preference. The developers of this app are committed to quality and providing a great user experience. All feedback is taken on board and we try to respond to all emails quickly. Digital World Clock. Interactive digital clock app with times from all time zones in the world. The app integrates with the charm settings for easy searching of clocks by cities or time zones. Manage live clocks using app bar buttons. Live tile update for first two clocks in every minute. The app has comprehensive DST support for time zones.